Manage autorelease version through dedicated file

[mara004]

Don't hardcode the current release versions of pdfium and pypdfium2, use dedicated autorelease files instead. Also consider encoding the install commit hash of pypdfium2 for definite identifiability ("release" or previous commit hash for autorelease commits).

[mara004]

For the library, I also think using a yaml/json version data file would be good, that's much nicer for API-level writing. We can still have a version.py file that reads in the yaml/json file.

[mara004]

done